The standards of the CMMB technique adapt to broadcasting service frequencies in the frequency range from 30 MHz to 3000 MHz, national roaming can be implemented by a broadcasting system of multimedia signals of satellites and/or terrestrial wireless transmitting televisions, broadcasts and data information, etc., and the transmission technique uses a mobile multimedia broadcasting technique Satellite Terrestrial Interactive Multi-service Infrastructure (STiMi) technique.
With the development of mobile multimedia services, the CMMB service presents three trends.
1. More and more diversified terminal equipment and the receiving devices. With the development of the mobile multimedia services, most of terminal equipment, such as mobile phones, Personal Digital Assistants (PDA), MP4s, digital cameras and laptops, etc., receive multimedia service data via a built-in CMMB receiving device, and display multimedia service data to the user. In addition, a part of receiving devices, such as data cards and netbook modules, etc., acts as an independent function device rather than is built in the terminal equipment, and such receiving devices can be connected to the display terminals, such as computers/laptops, etc.
2. The diversification of service types. With the development of the mobile multimedia services, the focus of the next step is to improve the multi-service support of CMMB terminals. Besides providing the basic audio and video services, CMMB shall also provide varied data services including browsing news, inquiring traffic information, shopping, advertising and interaction, etc., and such fresh and abundant service experience will obtain wider and wider attentions and applications.
3. The commercialization of service operations. With the development of the mobile multimedia broadcasting service, operators begin to perform the scrambling control on multimedia services, namely, the Conditional Access System (CAS) is added into the CMMB for controlling the user to receive services, and that is, only the user with the specified authorization can enjoy the provided corresponding service, which is the key point in implementing the personalized services. The basic object is to perform authorization control and authorization management on the user in the service operation, thereby implementing the paid service of the service system.
According to the three trends mentioned above, the receiving device connected with computer equipment, such as laptops, etc., will attract more and more attentions and be applied wider and wider. However, after general receiving device receiving the code streams of multimedia service data, there are two ways of descrambling and presentation processing on the code streams:
(1) the receiving device is only in charge of receiving the mobile multimedia broadcasting service, transmitting the data code stream to the computer equipment side where the descrambling processing and presentation of the multimedia service will be performed;
(2) the receiving device is in charge of receiving the mobile multimedia broadcasting service, and performing the descrambling process and then sending the descrambled data to the computer equipment side for presenting the multimedia service.
In the above way (1), in the condition of the user authentication module or the conditional receiving module being located in the receiving device, it will be involved that the key information needed in descrambling will be transmitted to the computer equipment side, which has certain unsafe factors.
In the above way (2), since the descrambled data are directly sent to the computer equipment side, other information like multiplex subframe header information in a plurality of multiplex subframes will be lost, which brings troubles to the data processing at the computer equipment side. Sometimes, the computer equipment also should read the multiplex subframe header information from the receiving equipment multiple times.